Research On Cooperative Spectrum Sensing And Optimization Technologies In Cognitive Radio Networks

In recent years, with the development of wireless communication technology, the demand forthe limited spectrum resources is increasing. Further, because the static fixed allocation policy isused in conventional radio spectrum resources allocation, in that case, unauthorized users can notcommunicate using the licensed frequency. Cognitive radio technology is a solution to the conflictbetween limited resources and service needs. It can find the spectral hole through the use ofspectrum sensing, and make use of spectrum resources through spectrum sharing opportunistically,which can improve the utilization of idle spectrum bands. The cooperative spectrum sensingtechnology, which can offset the effects of multipath fading, shadow effects and receiveruncertainties and other unfavorable factors, can improve the performance of spectrum sensing.The paper studies cooperative spectrum sensing from different aspects. Firstly, cooperativespectrum sensing results obtained is inseparable from the integration of the sensing data frommultiple users. Several commonly used data fusion methods are introduced, and the improvedmethods are cited. The fusion method based on D-S evidence theory is described. And in order toreduce the occupied channel bandwidth, a quantified cooperative spectrum sensing scheme basedon double threshold D-S evidence theory is raised. The data obtained in this way results in littledifference with the original method, but it is better than the traditional method of hard decisions.Secondly, based on centralized cooperative spectrum sensing method, for the problem whensome cognitive users far from the fusion center could not report sensing data to the fusion center, acooperative spectrum sensing methods based on clustering and multi-hop is raised. Clusteringmethod can reduce the occupancy of the reporting information on the channel, and the multi-hopway is to use forwarding method to relay the data of other cognitive users. Chair-Varshney rule isused for the judgment of primary user signal. The error probabilities of ooperative spectrum sensingcan be greatly reduced.Lastly, the system parameters to optimize cooperative spectrum sensing are analysed. Theoptimal values of the sensing time and the number of users in cooperative spectrum sensing indifferent conditions of detection probability and false alarm probability are discussed, with theutility function based on the system resource utilization efficiency and normalized throughput. Afast way to find the optimal value is proposed, making cooperative spectrum sensing system get thebest performance.